Robert Bly once said that to write a line of poetry requires two hours. Not so much for the actual writing. Not even for the inspiration. Though certainly for the revision. As well as compression and redistillation. And more revision.
His estimate, to me, seems quite optimistic.
I’m thinking it can be applied to many more examples of where human creative action is involved, too.
Go ahead, name one where you wish you had more time for the project.
Jnana's Red Barn 